Carpet is typically comprised of fiber tufts, a primary backing, an adhesive material, and optionally, a secondary backing. In the usual mode of manufacturing carpet, the fiber tufts are tufted through a woven or non-woven fabric which is the primary backing. The part of the tufts on the exposed surface of the carpet comprises face fiber. A latex-based adhesive is applied to the back of the tufted structure to lock in the tufts. Next a woven secondary backing is attached to the back of the primary backing to give the carpet added dimensional stability as well as to provide for additional tuft bind.
Usually the very edges of this structure have no fiber tufted through the primary backing for a width of typically about 1.75 to 4.5 inches. These edges are parallel to the machine direction of the carpet manufacturing process and are used to guide the carpet through the machinery by means of tentor pins in the machinery which pierce the edge of the carpet and hold it under tension. As a final step in carpet manufacturing and prior to rolling up the carpet for sale, these two, 2 parallel edges, having served their purpose, are trimmed from the carpet, producing carpet selvage waste. Such selvage waste is typically about 3 to 6 inches in width and has a small portion of tufts, typically about 1.25 to 4.25 inches in width, at one edge. The selvage waste is typically baled and sent to a landfill.
Carpet selvage waste has long been acknowledged in the carpet manufacturing industry as a serious waste issue. Because the carpet industry is concentrated in north west Georgia, most of the selvage waste produced in North America goes to one landfill, the Dalton-Whitfield County landfill. This landfill currently accepts about 50,000 tons of post-consumer selvage waste from carpet mills each year. In fact, the Dalton-Whitfield County landfill accepts so much selvage waste that they have actually devoted a special section of the landfill to dispose of this waste.
Several years ago, Waste Conversion Systems of Georgia proposed a plan to build a waste-to-energy plant in Calhoun, Georgia to deal with the problem. The plant was built, however the plan ultimately ended in an environmental tragedy when the plant and 1.5 acres of carpet selvage waste caught on fire. About 250 people were evacuated from their homes because of the resultant smoke. It took more than a week to fully extinguish the flames of this fire.
Carpet selvage itself has little or no value as a composite. Its disposal costs the carpet mills about $30/ton. Carpet selvage is however made of valuable materials. The primary and secondary backings are usually polypropylene, the fiber tufts are usually nylon 6, nylon 66, polypropylene, or polyester, while the remaining material in the selvage is mostly calcium carbonate and styrene-butadiene-rubber (SBR) latex. The value of these materials is realized only when they are segregated from one another and available for reuse.
Surprisingly, little work has been done to recover value from the carpet selvage waste stream. In U.S. Pat. No. 4,028,159 a process directed to carpet selvage is taught wherein selvage is heated to produce a mixture of meltable resins which is separated from any solid residue and then used in the adhesive mixture in subsequent carpet manufacture. This melt filtration process produces recovered polymer which has been significantly degraded, adversely impacting the recovered polymers' physical properties. This process would also produce air emissions with high organic content. Finally, while the resulting mixed resin may be used in carpets with hot melt adhesive backings, it is not useful in a typical SBR latex-backed carpet, and the mixed resin has little value if sold on the waste market.
There is a modestly larger body of art dealing with the recycling of whole carpets, whole carpet being carpet which has not been subjected to any mechanical segregation. There are two general categories of methods for reclamation of whole carpets, including carpet scraps. One category includes multiple mechanical steps including shredding, grinding and other means of overall size reduction followed by air elutriation and/or hydrocyclone segregation and/or screening and/or beating to effect segregation of the different components of the carpet waste. This category is exemplified by U.S. Pat. Nos. 5,230,473, 5,535,945, 5,497,949, 5,518,188, commonly-assigned U.S. Pat. No. 5,722,603, BP 1,349,000, and DE 3,343,788 A1. A common problem with these processes is that the stream of segregated carpet tufts is contaminated with residual latex and/or primary backing materials. Furthermore, none provide for the automated identification of the face fiber type as part of the process or reclamation. In addition, in the instance of U.S. Pat. No. 5,230,473, carpet selvage is too narrow for the application of the brushes described in the patent. DE 0,681,896 A1 teaches a process to recover highly pure fiber tufts and backing materials from broadloom carpet by first grinding the carpet then using a series of centrifuges to segregate the materials based on specific gravity. While this technique is technically feasible for use on carpet selvage waste, it would be too costly to install such a system at each carpet mill.
A second category of processes in whole carpet reclamation include depolymerization as a means of segregation from mixed components after various mechanical steps. U.S. Pat. No. 5,169,870, and commonly-assigned patents U.S. Pat. Nos. 5,656,757, 5,457,197 and 5,681,952 exemplify the use of a depolymerization step in whole carpet reclamation. Generally these methods would be impractical and expensive for use in carpet mills to use on carpet selvage. Furthermore, none provide for the automated identification of the face fiber type as part of the process or reclamation.
Therefore there exists a need for an inexpensive system to recover each component of carpet selvage in a relatively pure stream which would allow the carpet mills to avoid or reduce the disposal fees associated with carpet selvage. Furthermore, they could generate significant revenue from the sale of these segregated materials.